Separation by solvent extraction has been used since ancient times to recover useful products otherwise bound in solid substrates, such as organic leafy materials, or other liquids that render the product less useful. The Chinese used hot water to extract tea flavours from tea leaves as early as 1000 B.C.
Solvent extraction is classified into two main categories; liquid-liquid extraction, and solid-liquid extraction.
Liquid extraction is used to separate two miscible liquids by use of a solvent that preferentially dissolves one of them. Where separation by distillation is not possible or impractical, such as when products cannot tolerate the high temperatures required (even under vacuum), or when two liquids have very close boiling points, then liquid extraction is one of the main alternatives.
For example, temperature sensitive penicillin is commercially extracted from a fermentation broth using butyl acetate as a solvent.
As another example, in lube oil fractions containing aromatics, paraffins and naphthenes, the aromatic compounds typically have poor viscosity-temperature characteristics for the desired applications. Since the unwanted compounds have similar and overlapping boiling point ranges, they cannot effectively be distilled. Instead, the aromatics are extracted from the mixture using a polar solvent such as phenol or furfural, leaving the preferred products behind.
Solid-liquid extraction, also called leaching, uses a solvent to extract soluble matter from an insoluble solid substrate. The use of leaching is widespread throughout a full range of industries; agricultural industries in particular, use leaching to produce many otherwise non-recoverable products. Many edible oils are produced using solvent extraction to recover the oils held within the grains for example, canola oil from canola seed.
Table 1 below lists some well-known commercial and industrial applications of solid-liquid solvent extraction processes.
TABLE 1Examples of Solid-Liquid Solvent Extraction ProcessesProcessSoluteSolventSolidBeer productionMalted Barley ExtractWaterBarley GrainTea BrewingTea FlavourWaterTea LeavesCoffee productionCoffee FlavourWaterCoffee BeansSoybean EdibleSoybean OilHexaneSoybeansOil productionCanola OilCanola OilHexaneCanola SeedsproductionSugar productionSugarWaterSugar BeetsBayer process forAluminumSodiumBauxite OreAluminum metalOxideHydroxideproduction
During the drilling of a well, for example for gas or oil, drilling mud is typically pumped down the drill string through a drill bit. The drilling mud simultaneously cools the bit and carries drill cuttings up the well bore. Drilling mud is typically comprised of a fluid (or fluids), and mixture of additives which can be either fluids or solids, forming a useable drilling fluid.
One of the many functions of drilling fluid is to help carry away solid debris that forms during the drilling operation. Shales, clays, and formation debris continually slough off the walls of the well bore and into the drilling fluid. These cuttings hinder drilling fluid performance if allowed to accumulate. The accumulation of Low Gravity Solids (LGS) in an active drilling mud system is of significant concern to drilling well operators because they contribute to increased wear of high volume circulating equipment, they can cause the drill string to become differentially stuck in porous formations leading to expensive drilling downtime, and they contribute to reduced rates of drilling penetration, commonly known by those in the industry as the Rate of Penetration (ROP). LGS are continuously removed from the drilling operation by first carrying them to the surface in the mud, followed by removal at the surface.
The current state of the art for on-site drilling waste management is to recover drilling fluid from the cuttings using a combination of shale shakers, and decanter centrifuges. They operate on the principle of separation by mass density difference between the drilling fluid and the cuttings. Shale shakers can induce artificially high gravitational accelerations up to approximately 4 to 8 g, which aid the otherwise terrestrial 1 g acceleration used in conventional settling. Rotational velocity used in decanter centrifuges can induce accelerations of several thousand times that of terrestrial gravitational acceleration. The recovered drilling mud is recycled back to the drilling operation.
Despite many improvements to many different types of drill site cuttings treatment equipment throughout the well-established drilling industry, there remains a waste stream of drill cuttings that contains some drilling fluid held within the solids.
Accordingly, there is a constant search for new technologies and improvements to existing technologies to increase the efficiency and effectiveness of reclaiming and recycling processes.